1. Field of the Invention
The present invention relates to a light guide plate and an illumination apparatus including the light guide plate, and more particularly to a light guide plate which can obscure extracting elements for extracting light and to an illumination apparatus including the light guide plate.
2. Description of the Related Art
An illumination apparatus is known which uses a light guide plate and a light source disposed such that the light source faces a side surface of the light guide plate, as disclosed e.g. in JP 10-160938A. In the illumination apparatus, light that has been emitted by the light source travels in the light guide plate while repeating reflection at a pair of main surfaces of the light guide plate. A patterned diffusing material is provided on the back-side main surface of the light guide plate. The traveling direction of light traveling in the light guide plate is changed by the diffusing material, whereby the light will be incident on the main surface of the light guide plate at an angle less than the critical angle of total reflection and, therefore, exits the light guide plate via the main surface. Thus, the diffusing material functions as extracting elements for extracting light from the light guide plate. The pattern of the diffusing material is so determined as to be capable of achieving a desired distribution of the amount of exiting light along the light guide direction. In a typical example, when it is intended to make uniform the amount of exiting light from various points along the light guide direction, the pattern of the diffusing material is determined such that the area of the pattern increases with distance from the light source in view of the tendency of the amount of exiting light to decrease with distance from the light source.
However, an illumination apparatus that uses such a conventional light guide plate has the problem of visible appearance of a diffusing material for controlling the amount of exiting light from various points on the light guide plate. Especially when a diffusing/reflecting material is provided in a pattern, the pattern of the material will be perceived. This places limitations on the range of use of the conventional illumination apparatus because of problems in terms of appearance, such as deterioration of the design and a loss of high-grade appearance.